Do Any of You Freshwater Flush Your Engine?

[Art]

It has been recently that the Navy found some aluminum alloys that work better than zinc. Here is a write up on it. Maybe not the whole story but certainly part of it.

Aluminum anodes are rapidly replacing zinc for use on ALL hull materials. With the recent advent of alloys developed by the US Navy, anode aluminum is very different from the aluminum alloys used for boat hulls, outboards, and stern drives. These "mil spec" aluminum anodes are more electrically active and protect better than zinc, plus they last longer! Aluminum has been used in the offshore industry for years to protect installations where long-term corrosion protection is essential. Aluminum anodes also use a much less toxic activator – which makes them better for the environment. To top it off, aluminum anodes are really the only choice that will work in both brackish AND salt water. So if you keep your boat in a place that is exposed to both (such as at the mouth of a river that empties into the ocean) you should definitely be using aluminum. Aluminum has become the anode of choice for the US Navy, as well as for large commercial fleets. This is due to the money they save (aluminum anodes last longer so ships go longer between replacements) and because aluminum is so much lighter that they can help provide better fuel economy in larger fleets. Aluminum anodes are available for both recreational and commercial applications.

Thanks, Dave. Sounds good for using aluminum as anode. Do you know where that interesting info is quoted from?

 

[Comodave]

I used The Google.

 

[firehoser75]

https://performancemetals.com/pages/sacrificial-anodes-faqs
Art, and others looking for info on aluminum anodes:
See attached. Yes, this is a company that makes and sells aluminum anodes, but there are also links to other sources.
There are not full scientific studies done on everything (and most people don't always require them), as they are expensive (and time consuming) to conduct. If the Navy developed and is switching to aluminum anodes, that sounds like a relatively "trusted" source (to me).
Anyway, each boater has to decide for themselves what anode type they want to use. I think Dave and others are just trying to offer info to help make the best decision for your (the collective your) situation. However, it does appear (from various sources) that using zinc is not recommended for freshwater use (even periodic FW use).

 

[lwarden]

I've got an update on this... From my previous test where I did flushing of the raw water on both engines with the seacock open I surmised that the pump flow was still pulling in a significant amount of salt water. As such, the flushing wasn't effective (and zinc anode erosion was similar to the control non-flush test). This winter I replaced the anode with zinc again and started flushing with the seacock closed so there can only be fresh water in the system. This is a bit tricky since I have to quickly shut off the water and then engine as closely as I can to avoid burning an impeller. I have a plan for a better flush system... more on that later.

Anyway, the update is that after doing these flushes if several weeks go by upon startup there is a scatter of small white particles, probably a mm or two in size coming out both exhaust for the first minute. So presumably this is the coating on the zinc blowing off. Now, the question is: does that mean the zinc is now cleaned off sufficiently to provide protection? Hard to know but I may pull one before starting the engine to see what it looks like before and after startup and will post the pictures.

The obvious suggestion is to switch to aluminum anodes, I suspect that will be next. Just not sure if I can leave the running gear and divers dream as zinc and have aluminum in the engine raw water path or do I have to change them all the Al?

 

[Comodave]

I've got an update on this... From my previous test where I did flushing of the raw water on both engines with the seacock open I surmised that the pump flow was still pulling in a significant amount of salt water. As such, the flushing wasn't effective (and zinc anode erosion was similar to the control non-flush test). This winter I replaced the anode with zinc again and started flushing with the seacock closed so there can only be fresh water in the system. This is a bit tricky since I have to quickly shut off the water and then engine as closely as I can to avoid burning an impeller. I have a plan for a better flush system... more on that later.

Anyway, the update is that after doing these flushes if several weeks go by upon startup there is a scatter of small white particles, probably a mm or two in size coming out both exhaust for the first minute. So presumably this is the coating on the zinc blowing off. Now, the question is: does that mean the zinc is now cleaned off sufficiently to provide protection? Hard to know but I may pull one before starting the engine to see what it looks like before and after startup and will post the pictures.

The obvious suggestion is to switch to aluminum anodes, I suspect that will be next. Just not sure if I can leave the running gear and divers dream as zinc and have aluminum in the engine raw water path or do I have to change them all the Al?

If you are leaving freshwater in the engines then you should not be using zinc anodes. Better to use aluminum. As to what hull anodes to use, again I would use aluminum. They work in any water. However the engines and the hull are 2 different bodies of water so you can use dissimilar anodes. But why not just go with all aluminum anodes? They are better for the environment than zinc anodes as well.

 

[Caballero II]

Every time,well 95 % of the time,unless I tie the boat up after midnight and have been drinking all day

I try to do this religiously, but occasionally it might take a day or three. I will say that doing this has greatly decreased the need to change zincs, to almost no need.

 

[Caballero II]

I really don’t understand the thinking of people that still insist on using zinc anodes. When aluminum will work everywhere. Sorry, I just don’t get it…

Well, just asking because I think I've read it somewhere. Are Al anodes as efficient in saltwater as zincs, and what is the efficiency delta? My admittedly sketchy memory says that Al zincs aren't as efficient in salt water, by a good margin. Also, I've never see Al anodes in my local chandlery.

 

[DDW]

Current thinking is that AL is better than ZN in salt water. Slightly better galvanic potential. Also they last longer.

I will say that if you fresh water flush, you will find more wastage of engine AL anodes than ZN anodes. I think that is because the ZN aren't doing much to protect anything in the fresh water.

 

[Caballero II]

Well, that's good to know. Love to see the peer-reviewed article, or something equal supports that. I'll look into Al "zincs". As written, we try to fresh-water flush after each voyage. I don't know where/when the Al anode deal became a thing. If true, works for me.

 

[Comodave]

I try to do this religiously, but occasionally it might take a day or three. I will say that doing this has greatly decreased the need to change zincs, to almost no need.

That is probably because when zinc is in freshwater it develops a coating that stops it from working to protect the metals. People here in freshwater will tell me that their zinc anodes last for years, because it is freshwater so zincs don’t work. Zinc will last for years because it isn’t working.

 

[backinblue]

Dave is correct, but also makes an important point worth noting. Your goal shouldn't be to have "zincs" that never need replacing. That just means they are not doing anything. "Zincs" that are wearing is a good thing.

 

[Mischief Managed]

My 3208TAs have a known issue where cold raw water and warm and humid air can cause condensation in the after coolers that drips water into the #6 intake port. I added fresh water flush that plumbed into my pressurized hot fresh water on my boat. The goal is to replace the salt water with fresh water to make the raw water components last longer, and to prevent condensation in the after coolers by using HOT fresh water. Have not tested it yet, but it's all built and installed. Will certainly make Winterization easier.

 

[sunchaser]

Fresh water flushing one’s raw water system does no harm. But are presumed benefits to impacted systems valid or imagined in all cases vs just a few?

 

[rslifkin]

Fresh water flushing one’s raw water system does no harm. But are presumed benefits to impacted systems valid or imagined in all cases vs just a few?

It depends on the system. Some growth and buildup that can form in the system may be reduced though. When I first brought our boat into fresh water, the morning starts after the first few overnights involved a bit of whitish powdery junk in the exhaust water for a few days. After a couple of days, we didn't get any more, but the engines were running slightly cooler under load compared to when we started the trip. I'm thinking some salt buildup in one of the coolers or the heat exchanger was dissolving in fresh water.

 

[Comodave]

When you compare an all time freshwater boat to a saltwater boat there is a marked difference. Our current boat has been freshwater all its life and the engines don’t have the rust on them that a saltwater boat would have at 25 years. Also all the metal on the boat is in much better condition than a saltwater boat would. Freshwater flushing must help but you absolutely do want your anodes to be wasting away. If they are lasting for ever then they aren’t doing anything.

 

[Bacchus]

It depends on the system. Some growth and buildup that can form in the system may be reduced though. When I first brought our boat into fresh water, the morning starts after the first few overnights involved a bit of whitish powdery junk in the exhaust water for a few days. After a couple of days, we didn't get any more, but the engines were running slightly cooler under load compared to when we started the trip. I'm thinking some salt buildup in one of the coolers or the heat exchanger was dissolving in fresh water.

When I read discussions about FW flushing I think about the Navy practice of mothballing ships where there is a reversal of salt & fresh water with the tides.
As a kid riding up/ down the Hudson I was curious seeing the mothballed fleet anchored somewhere around Bear Mtn? I never understood the reason until,mas a boating adult, I read more about the reason why. Don't know a lot about the biological details but apparently organisms that build up in salt water are affected by the fresh water and the opposite as well. So, the reversing FW / SW significantly reduces the hull growth.
I would think there would be some similar affects internal to the cooling system as there are external to the hull?
Maybe others know more about the details?

 

[backinblue]

Good thought Don. My home port is in a tidal river so I convince myself that there are times when the tide is going out as I'm returning home that I get a freshwater flush. I'm pretty close to the sound so probably still pretty salty I think. I can tell you that I get a lot of barnacles in the course of a season.

 

[Mischief Managed]

update on my fresh water flush system

I have used mine for the 2023 season so far and have noticed a dramatic reduction in anode wear. They are still wearing, but I could probably get 3 seasons from them instead of 1/2 a season like I was getting before the flush system was installed on my CAT 3208TAs. They cost about 140 bucks to swap twice a season so the savings should add up quickly and I don't have to worry about condensation forming on my after coolers and dripping into my #6 cylinders anymore.



After every run, I start by opening the ball valve on the flush system and running a gallon of hot, fresh water into the system through a tee I installed between the strainer and the raw water pump (very near the water pump) with the engine off and the raw water seacock open. This pushes salt water out of my hoses and strainer, limiting the amount of salt water that will mix with the incoming fresh water. After a gallon has flowed, I simultaneously start the engine and close the seacock so that the engine can only pull hot fresh water into the raw water pump. I let the engine run until 3 more gallons has flowed and then simultaneously shut the engine down and close the flush ball valve. I then slowly open the seacock (there's typically a little pressure differential between the ocean and the raw water pump inlet after flushing) and repeat on the other engine.



In addition to the raw water flush plumbing, I also installed a water flow counter and engine starter and fuel stop buttons right by the seacock and flush valves. Both engines take about 5 minutes in total to flush and I can do the job while sitting comfortably in the ER after entering the ER from a very convenient entry behind a set of lift-up stairs in my galley (that is not convenient for much else to do with the engines).



I bet I spent less than $200 in materials to make the system. It's mostly Pex with silicone heater hose where flexibility is needed for reliability. We have not noticed a difference in lifestyle necessitated by the use of an extra 8 gallons of water after each engine run when we are living on the hook, but we do plan to install a water maker some day so that will become pretty much moot anyway. We carry 140 gallons of fresh water in our tank.

 

[Bacchus]

Dave
"have used mine for the 2023 season so far and have noticed a dramatic reduction in anode wear."

Wondering what composition anodes you are using?

If zinc, I'd venture a guess that you are not getting the protection or wear during the fresh water soak time. I can't think of a short term test to confirm but have to wonder if short term you have less anode wear but long term will show more heat exchanger wear ( assuming zinc assumtion is correct)